1. Field of the Invention
This invention is concerned with the management of a human airway in order to control respiration. More particularly, the invention concerns a device that brings an airway tube reliably and safely into communication with the laryngeal opening, the upper end of the trachea, which is the breathing passageway that leads to the lungs. The device seats in the throat immediately adjacent the laryngeal opening, tensions and erects the laryngeal opening, and seals with it to provide a channel through the airway tube for artificial ventilation of the lungs. In particular, the invention concerns a device that can accurately position itself laterally with respect to the laryngeal opening, that can accurately position itself in depth with respect to the larynx, and that can retain itself in position during operation.
2. Description of the Related Art
An airway device facilitates ventilation of the lungs of a person. The purpose of such a device is to provide an air pathway from an external air source, through the mouth, throat, and trachea, to the lungs. Additionally, some airway devices provide a seal with the throat of a person, which allows positive pressure ventilation and which may also prevent the leakage of stomach contents into the trachea (aspiration).
It is useful to divide airway devices into two categories: those that pass through the vocal chords and are commonly referred to as "tracheal tubes", and those that lodge in the throat, above the vocal chords, and are commonly referred to as "airways". We shall limit "airway" to refer to a device that provides a fluid pathway from outside the mouth of a person to a location above the vocal chords.
In the variety of airway devices that are available, some merely support the tissue of the pharynx (throat), particularly the tongue, creating a passageway so that air can pass by and into the pharyngeal space toward the laryngeal opening, which is the opening into the voice box. Other airway devices include a tube that provides an air channel to a location near the laryngeal opening. Still other airway devices add a sealing means to the distal end of the tube in order to provide some degree of sealing between the tube and the airway of the person.
A laryngeal mask is an example of a sealing airway device. U.S. Pat. Nos. 4,509,514; 4,995,388; and 5,355,879 are descriptive of a laryngeal mask. A laryngeal mask includes an inflatable doughnut-shaped balloon which, when inflated, circles the laryngeal opening and creates a fluid seal between the outside of the inflated balloon and the tissues in the pharyngeal structures of the throat that surround the larynx.
Another sealing airway device, described in U.S. Pat. No. 5,513,627, includes an inflatable balloon fixed on the distal end of a tracheal tube that is inserted into and inflated within the trachea, forming a seal against the interior walls of the trachea.
In the first three cross-referenced patent applications, all assigned to the assignee of this application and incorporated in their entirety by this reference, a sealing member is mounted near the distal end of an airway tube to seal directly with the rim of the laryngeal opening, portions of the epiglottis, and the sidewalls of the larynx. This unique airway creates a fluid seal directly with the larynx.
Airway devices that seal with the larynx or pharyngeal structures surrounding the larynx need to be accurately positioned with respect to the larynx. However, it is common knowledge to the clinician that it can be very difficult to accurately position an airway device with respect to the anatomy of the larynx, which can be highly variable and extremely flexible.
Positioning of an airway device with respect to the larynx is difficult in both the lateral axis and the cephalad-caudad axis (which is also called the "depth" axis). Further, once correctly seated, it can be very difficult to maintain an airway device in the correct position. Maintaining the correct position is important for several reasons. First, proper ventilating of the patient is critical to patient safety and care. Second, anesthetic gases are intended to be delivered to the patient's lungs and a poorly aligned airway could result in the gases being introduced into the patient's esophagus or into the operating room environment. Finally, should there be any regurgitation of contents from the patient's stomach, the airway seal must be secure to prevent the contents from entering the patient's lungs.
The larynx is made of several flexible cartilages and membranes which span the cartilages. The laryngeal opening looks like the open end of a pipe that has been cut off at an angle of roughly 45.degree.. The acute, angled, pointed edge of the laryngeal opening is formed by the epiglottis and positioned on the anterior (front) side of the throat (also called the pharynx). The flexible epiglottis is a cartilage that is highly variable in shape and size. The epiglottis can easily be bent backward to cover the laryngeal opening if pressure or a stimulus is applied on its anterior side. The obtusely angled posterior edge of the laryngeal opening is formed by the two arytenoid cartilages. The arytenoideous muscle, which is stretched between the arytenoid cartilages, forms the base of the inter-arytenoid notch. The sidewalls of the laryngeal opening are formed by the ary-epiglottic folds. These are flexible, compressible membranes, stretching from the arytenoid cartilages posteriorly to the epiglottis anteriorly. The larynx then, is a flexible, collapsible structure that stands up like an angled pipe in the hollow of the pharyngeal space. Manifestly, the laryngeal opening, especially on its anterior side is not a firm or consistent structure on which to position an airway device.
All of the sealing devices presently align themselves laterally with respect to the larynx by filling the pharyngeal space (throat) with an inflatable balloon or a resilient foam pad. The assumption is that the larynx lies in the midline of the pharynx and therefore an inflated balloon will center the airway in the pharyngeal space, which should approximately align with the laryngeal opening. Generally this assumption holds for pharyngeal airway devices. Pharyngeal airway devices loosely surround the laryngeal opening and form a seal on the pharyngeal structures. Therefore, precise orientation with the laryngeal opening is not necessary. On the other hand, laryngeal airway devices such as those described and illustrated in the incorporated patent applications, require very precise orientation with the laryngeal opening if they are to form a dependable seal. Lateral alignment with the pharyngeal structures is not accurate enough for reliable lateral alignment with the laryngeal opening.
Accordingly, there is a need for an airway device that can accurately position itself in the lateral dimension with respect to the laryngeal opening.
Anterior to the larynx is the vallecula, which is the angle formed between the anterior side of the epiglottis and the tongue. The vallecula has served as a positioning point for the introduction of laryngoscopes and other introducers. However, the vallecula is not a practical end-point for positioning laryngeal airway devices at or within the laryngeal opening, because it is outside of the laryngeal opening, on the opposite side of the epiglottis from the laryngeal opening.
On the posterior side of the larynx is the hypo-pharynx, which is the smooth lower part of the throat that leads to the esophagus and stomach. There are no protuberances or pockets on the hypo-pharynx that can serve as an end-point on which to position an airway device with respect to the depth axis of the laryngeal opening.
Similarly, the hypo-pharynx on both sides lateral to the larynx describes a substantially smooth taper down to the esophagus, without protuberances or pockets. Therefore there is no good end-point laterally, on which to seat an airway at or in the laryngeal opening.
Accordingly there is a need for an airway device that can accurately position itself along a depth axis (cephalad-caudad) with respect to the larynx.
Assuming correct positioning of an airway device on a lateral axis and on a depth axis with respect to the laryngeal opening, it becomes necessary to retain the airway device in that correct position, accurately oriented with the laryngeal opening over a prolonged period of time. Again, the anatomy of the throat is not helpful in this respect. The hypo-pharynx is substantially funnel-shaped and it would seem obvious that a funnel-shaped airway device, inflated within the funnel-shaped hypo-pharynx would naturally seek to eject itself from the seated position.
Airway devices that seal against the angled laryngeal opening are inherently unstable. The sealing surface of the device must be angled to match the natural angle of the laryngeal opening. Abutting these two angled surfaces also creates an unstable situation in which the airway device may be naturally ejected from the correct position.
The angle of the vallecula between the anterior side of the epiglottis and the tongue is oriented opposite the direction necessary to retain an airway device in position with respect to the laryngeal opening. Accordingly the vallecula does not afford an anchoring or retention site.
The tongue is highly flexible and has no protuberances which can serve as anchors on which to retain an airway device. Most airways present smooth surfaces in order to minimize trauma to the delicate tissues of the throat, larynx, and trachea. The smooth flexible surface of the tongue cannot interact with the smooth surface of an airway device to provide any appreciable amount of "grasping". Therefore, the tongue would seem not to present an opportunity for airway device retention.
The pharynx and hypo-pharynx on the posterior and lateral sides of the larynx also present smooth tissue surfaces without protuberances or angles which can serve to retain an airway device.
At present, an airway device is most frequently retained in position by simply taping the air tube of the device to the face of a person. This is not an ideal or accurate solution to the problem of positioning because the tape may become loose or dislodged, because the skin of the face is very mobile, and because the proximal end of the tube (where the tape is usually applied) is not consistently or precisely oriented with respect to the distal end of the tube, where the airway device is located. Moreover, the shape of the tube may change during airway device operation, further changing the relationship between its proximal and distal ends. The net result may be a movement of the distal end of the tube, which can dislodge the airway device from its correct position.
Accordingly, there is a need for an airway device which can retain itself naturally and accurately in a correct position with respect to the laryngeal opening.